1. Field of the Invention
The present invention relates to a method for forming a thin film on a substrate, and more particularly to a method for forming a silicon dioxide film using atomic layer deposition (ALD).
2. Description of the Related Art
As the sizes of microelectronics devices continue to become smaller, the qualities of silicon dioxide films that are used as gate oxide films and dielectric films of electric field effect transistors in semiconductor devices have correspondingly become increasingly important.
Conventionally, in the fabrication of semiconductor devices, silicon dioxide films are mainly formed using thermal chemical vapor deposition (thermal CVD), low pressure CVD (LPCVD), and plasma-enhanced CVD (PECVD). Among these conventional techniques, thermal CVD provides good step coverage but must be carried out at a relatively high temperature. PECVD provides a high deposition rate at a low temperature but poor step coverage. For these reasons, these CVD methods have been used only in a limited manner for silicon dioxide film formation. Recently, as semiconductor devices become highly integrated, a short channel effect caused by high temperatures in CVD methods has also been recognized as a major problem. Therefore, low temperature silicon dioxide film formation methods are required. In addition to the above problems, as the step-to-step height on a semiconductor substrate increases, step coverage becomes poor and a significant undesirable pattern loading effect is caused. Therefore, there is a need to develop improved silicon dioxide film forming methods.
In order to solve the aforementioned problems, there have been proposed methods for forming a silicon dioxide film using atomic layer deposition (ALD). An exemplary method for forming a silicon dioxide film is disclosed in U.S. Pat. No. 6,090,442 in which an ALD process based on SiCl4 and H2O is used. However, a SiO2 monolayer formed after one ALD cycle has been found to have a low packing density, and furthermore the deposition rate for such process is very slow. For these reasons, a desired throughput requirement in a semiconductor device manufacturing process is not satisfied by this ALD technique. Meanwhile, SiCl4 has four Si—Cl bonds per Si atom. When low temperature vapor deposition is carried out, H2O has been found to attack the Si—Cl bonds to form O—H bonds. As a result, a large amount of the O—H bonds remain in such an ALD-formed silicon dioxide film, resulting in an undesirably porous silicon dioxide film.